1. Field of the Invention
The present invention relates to a communication system having a communication apparatus and an information server capable of performing communication in first and second communication modes.
2. Description of the Related Art
Conventionally, in a communication system having a communication apparatus such as a mobile terminal that transmits and receives text data comprising character data and multimedia data such as sound, images or moving images, and an information server, the communication mode which is used in information acquisition of the communication apparatus from the information server is selected and fixed in requesting the information, and the selected communication mode is not changed until the information acquisition is completed.
There is known such a communication mode as one of communication modes having a plurality of channels as communication paths that when during communication in a normal communication channel the information transfer rate is insufficient, in addition to the normal communication channel, additional connection to a second channel is carried out, and in response to a request to disconnect the connection to the second channel, changeover of communication path is automatically carried out so that only the normal communication channel is used.
However, the communication channel switching control, which is possible in communication modes having a plurality of channels as communication paths, cannot be applied to communication modes having only one communication channel.
Moreover, in conventional communication systems capable of performing communication in a plurality of communication modes, the communication mode can be switched before a request for information acquisition is made, however, after a request for information acquisition is made, the communication mode is fixed to the one selected when the request for information acquisition is made, and the communication mode cannot be changed unless information acquisition is temporarily stopped and the communication condition is re-connected. For this reason, in the conventional communication system, even when information to be acquired from the information server can be more efficiently transferred in terms of the communication time, communication charge or the like in a communication mode other than the communication mode selected when the request for information acquisition is made, it is difficult to perform switching of communication mode and restore connection conditions, and therefore, the communication mode is seldom switched.
There is known a communication mode in which although the maximum rate of information transfer is low, the communication charge is made according to the amount of transmitted and received information. This mode is advantageous for viewing multimedia data because the data is viewed after its acquisition, however, a great deal of communication time is required to download music information data or the like.
Moreover, there is known a communication mode in which the information transfer rate is higher than that of the above-described communication mode and data can be acquired in a short time. This mode, however, is unsuitable for viewing multimedia data, which is viewed after its acquisition, because the communication charge is made according to the communication time.
Japanese Unexamined Patent Publication JP-A 11-275143 (1999) proposes a communication control method for a communication apparatus that performs data transmission/reception through a radio interface with a data communication terminal connected to a sub apparatus through a data communication apparatus, and performs data transmission/reception through a digital network interface with a data communication terminal connected to a digital network through a data communication apparatus. According to this communication control method, although the communication mode switching control is performed, it is necessary to newly set communication conditions for a selected communication mode.